In patients being evaluated for known or suspected ventricular arrhythmias, the presence of T wave alternans measured during an exercise stress test using the spectral method of the CH2000 Cardiac Diagnostic System and HisResECG electrodes is equivalent to or better than the signal-averaged ECG (SAECG)measured by using the Pred.II (K#915760) or successor systems as a measure of increased susceptibility to ventricular arrhythmias.